Carbonate rocks are the most important sedimentary rocks since they hold almost 60

This study marks the first detailed depositional, diagenetic and organic geochemical investigation of Jurassic Isha Formation in North Waziristan, Khyber Pukhtunkhuwa, Pakistan. Detailed systematic sampling was carried out from exposed outcrop along the Mirali road in North Waziristan for microfacies analysis and diagenetic studies to unravel the depositional environment and diagenetic alterations. The oraganic maturity and hydrocarbon generation potential were assessed by total organic content and Rock-Eval pyrolysis. Outcrop analogue revealed that the formation predominantly comprises of thick to thin bedded oolitic fractured limestone, bioclastic and dolomitic limestone. In the petrography, a total of eight microfacies (MF1–MF8) were constructed and were directed different depositional enviroments. Based on the integrated field data and microfacies analyses, the Isha Formation is interpreted to be deposited on a homoclinal ramp particularly in peritidal, lagoon, and carbonate shoals. Sequences stratigraphic setup shows intervallic Transgressive and Regressive Systems Tracts. The TSTs are mostly grainstone and packstone facies whereas the RSTs are wackestone and mudstone microfacies which demonstrates a single 2nd order cycle and then multiple 3rd order transgressive and regressive cycles for the deposition of Isha Formation. The total organic content and Rock-Eval pyrolysis results were ploted on VanKerevlen diagram which indicate that the source rock potential fall within the type III kerogen. The HI versus Tmax and PI versus Tmax cross plots indicate that the formation lies within the zone of maturation, generation potentiality indicate that the formation has fair to poor potential and hydrocarbons are indigenous.

The porosity and permeability determine the reservoir quality of sedimentary rocks, which is fundamentally influenced by both depositional and diagenetic processes. The Jurassic carbonates are targeted in many regions for oil and gas exploration. The current study is carried out to elaborate on the diagenetic alterations and their effect on reservoir properties. A thick outcrop of the Jurassic Samana Suk Formation is studied in the Kahi section of Nizampur Basin Northwest Himalayas, Pakistan, to study and relate the trend of lithological variations and depositional settings. Field investigation revealed that the Samana Suk Formation is extensively distributed in the area and primarily made up of interbedded limestone and dolomite units. The original unaltered limestone has a thick-bedded and oolitic to bioclastic nature. Different types of dolomites have been recognized based on colour contrast and sedimentary features. Moreover, saddle dolomite cement, calcite cementation, and mechanical and chemical compaction have also been observed. The petrographic studies show different types of diagenetic alterations that affected the Samana Suk Formation, including micritization, bioturbation, mechanical and chemical compaction in the form of fractures and stylolites, various calcite cementation, which includes the various cement types that range from isopachous, blocky, granular equant, fibrous, and dog tooth cementation, along with dissolution that occurred in different diagenetic realms. Pyritization was rarely observed. Moreover, different phases of dolomites were identified, ranging in size and shape, i.e., finely crystalline to coarse crystalline and planar euhedral to non-planar anhedral. The stable oxygen isotope values of these dolomites show depletion from original marine signatures and suggest burial-related fault-controlled dolomitization events. Overall, diagenetic processes like dissolution, fracturing and dolomitization increased the reservoir potential. On the contrary, the overburden and cement precipitation result in decrease in the reservoir properties.

An integrated study of sediments was conducted to examine the facies architecture and depositional environment of the Cretaceous Pab Formation, Rakhi Gorge, and Suleiman Ranges, Pakistan. This research focused on analyzing architectural elements and facies, which are not commonly studied in sedimentary basins in Pakistan. To identify lithofacies, outcrop analysis and section measurement were performed. The identified lithofacies were then categorized based on their depositional characteristics and facies associations, with a total of nine types identified within a stratigraphic thickness of approximately 480 m. These facies were mainly indicative of high-energy environments, although the specifics varied by location. Sedimentary structures such as planar and trough crossbedding, lamination, nodularity, load-casts, and fossil traces were found within these facies, indicating high-energy environments with a few exceptions in calm environments. The identified facies were grouped into seven architectural elements according to their depositional environments: delta-dominated elements, including laminated shale sheet elements (LS), fine sandstone elements (SF), planar cross-bedded sandstone elements (SCp), trace sandstone elements (ST), and paleosol elements (Pa); and river-dominated elements, including trough cross-bedded sandstone elements (SCt), channel deposit elements (CH), and paleosol elements (Pa). These architectural elements, along with their vertical and lateral relationships, indicate a transitional fluvio-deltaic environment within the Pab Formation. In conclusion, by interpreting facies and architectural elements, it is possible to gain a better understanding of the depositional history of the formation and the distribution of reservoir units.

The present study deals with the depositional facies,diagenetic processes and sequence stratigraphy of the shallow marine carbonates of the Samana Suk Formation,Kohat Basin,in order to elucidate its reservoir quality.The Samana Suk Formation consists of thin to thick-bedded,oolitic,bioclastic,dolomitic and fractured limestone.Based on the integration of outcrop,petrographic and biofacies analyses,the unit is thought to have been deposited on a gentle homoclinal ramp in peritidal,lagoonal and carbonate shoal settings.Frequent variations in microfacies based sea-level curve have revealed seven Transgressive Systems Tracts(TSTs)and six Regressive Systems Tracts(RSTs).The unit has undergone various stages of diagenetic processes,including mechanical and chemical compaction,cementation,micritization,dissolution and dolomitization.The petrographic analyses show the evolution of porosity in various depositional and diagenetic phases.The fenestral porosity was mainly developed in peritidal carbonates during deposition,while the burial dissolution and diagenetic dolomitization have greatly enhanced the reservoir potential of the rock unit,as is further confirmed by the plug porosity and permeability analyses.The porosities and permeabilities were higher in shoal facies deposited in TSTs,as compared to lagoonal and peritidal facies,except for the dolomite in mudstone,deposited during RSTs.Hence good,moderate and poor reservoir potential is suggested for shoal,lagoonal and peritidal facies,respectively.

Dolomitization is a hot issue due to the fact that dolomitized successions host hydrocarbon reservoirs. Hence understanding the dolomitization process is very vital to anticipate the probable presence of dolomite bodies in the subsurface. Multi-phase dolomitization process can be best understood by investigating partially dolomitized carbonate sequences. Field observations, petrographic studies and geochemical analysis were used to understand the possible mechanism of dolomitization which reveals four replacive matrix dolomite phases (Dol-I, Dol-II, Dol-III and Dol-IV), veins and vug filling Saddle dolomite cement (SD) in partially dolomitized late Cretaceous Kawagarh formation Southern Hazara basin, North-West Himalayas, North Pakistan. Calcitization phases are also found associated with dolomite bodies including white calcite (WC) and twin calcite (TC). Brecciation, cataclastic deformation and stylolitization are other diagenetic modifications. Geochemical examination assisted in differentiating these various dolomite. Extensive range of depleted δ18O values (– 11.87 to – 4.23‰ V-PDB) of dolomites phases support multiphase dolomitization at numerous temperatures. Haro Thrust, along which the late Cretaceous Kawagarh formation is thrusted over Paleocene/Eocene rock units, has provide pathways to Mg-rich fluids from the underlying basinal sediments to form fault-related dolomites. In conclusion, burial hydrothermal dolomitization followed by fault related model may be the possible model that explains the mechanism for such type of dolomitization.

The late Cretaceous Kawagarh Formation has been investigated in terms of field observation, and petrographic analysis, to understand the petrography and its impact on the geotechnical properties. The Kawagarh Formation is well exposed among the upper Indus Basin, and has been studied by various workers in different aspects. Kawagarh Formation exposed in Kahi section of Nizampur Basin has been selected in this study to know the behavior of carbonate rocks for engineering purposes. Lithologically, this formation is composed of thick to medium bedded, highly fractured limestone, marls, and dolomitic limestone which has undertaken diagenetic alteration including dolomite, calcite veins, and stylolites. Followed by petrographic analysis which reveals that the Kawagarh limestone is mostly fossiliferous comprised of a large number of planktonic foraminifera fossils like Globotruncana Hilli and Globotruncana Linneana fossils. Furthermore, to know the impact of petrographic minerals on engineering behavior, mechanical properties in terms of uniaxial compressive strength (UCS) and uniaxial tensile strength (UTS) were also computed by using a universal testing machine (UTM). The resultant mechanical values lie in the strong compressive strength and suggest their usage for various construction purposes. Aggregate degradation tests including water absorption, specific gravity, aggregate impact value, Los angles abrasion, and soundness was also computed according to the International standard organization, ASTM (American Society for testing materials) and British standard. The aggregate values of the Cretaceous Kawagarh Formation are within the defined standard limits and can be used as an aggregate source for different construction engineering projects.

This paper reports the first detailed microscopic and geochemical investigations of multiphase dolomitization in Devonian Shogram Formation, North-Western Karakorum constraining nature and origin of dolomitizing fluids. Field and petrographic studies revealed 4 different types of replacive dolomites, which are (i) fine grained anhedral dolomite (D1), (ii) medium grained subhedral to anhedral dolomite (D2), (iii) medium grained euhedral dolomite (D3), and (iv) coarse grained anhedral dolomite (D4) along with cement phase saddle dolomite (SD). These dolomites had high Fe and Mn concentraions and low Sr content. Stable isotope studies indicated high light isotope δ18O values for D1 and D2, higher lighter isotope δ18O value for D3, and highest lightest isotope δ18O values for D4 and SD, respectively. Petrographical and geochemical data suggested that D1 and D2 are likely formed in compactional flow regime in early stages prior to chemical compaction at shallow burial depths, whereas D3 is formed in late diagenetic deep burial settings. Lastly, D4 and SD are formed from high temperature hydrothermal fluids. These fluids could be related to widespread tectonic activity in the Karakorum region during collision or post-collisional time. Reshun fault acted as an important pathway that channeled Mg-rich hydrothermal fluids from underlying strata into carbonates, which caused intense dolomitization.

In the present study, an attempt has been made to establish the relationship between diagenetic alterations resulting from magmatic intrusions and their impact on the reservoir properties of the Devonian Khyber Limestone (NW Pakistan). Field observations, petrographic studies, mineralogical analyses, porosity-permeability data, and computed tomography were used to better understand the diagenetic history and petrophysical property evolution. Numerous dolerite intrusions are present in the studied carbonate successions, where the host limestone was altered to dolomite and marble, and fractures and faults developed due to the upwelling of the magmatic/hydrothermal fluids along pathways. Petrographic studies show an early phase of coarse crystalline saddle dolomite (Dol. I), which resulted from Mg-rich hydrothermal fluids originated from the dolerite dykes. Coarse crystalline marble formed due to contact metamorphism at the time of dolerite emplacement. The second phase of dolomitisation (Dol. II) postdates the igneous intrusions and was followed by dedolomitisation, dissolution, and cementation by meteoric calcite. Stable isotope studies likewise confirm two distinct dolomite phases. Dol. I exhibits more depleted δ 18 O (-15.8 to -9.1‰ V-PDB) and nondepleted δ 13 C (-2.05 to +1.85‰ V-PDB), whereas Dol. II shows a relatively narrow range of depleted δ 18 O (-13.9 to -13.8‰) signatures and nondepleted δ 13 C (+1.58 to +1.89‰ V-PDB). Dolomitic marble shows a marked depletion in δ 18 O and δ 13 C (-13.7 to -8.5‰ and -2.3 to 1.95‰, respectively). The initial phase of dolomitisation (Dol. I) did not alter porosity (5.4-6.6%) and permeability (0.0-0.1 mD) with respect to the unaltered limestone (5.6-6.9%; 0.1-0.2 mD). Contact metamorphism resulted in a decrease in porosity and permeability (3.3-4.7%; 0.1 mD). In contrast, an increase in porosity and permeability in Dol. II (7.7-10.5%; 0.8-2.5 mD) and dolomitic marble (6.6-14.7%; 8.2-13.3 mD) is linked to intercrystalline porosity and retainment of fracture porosity in dolomitic marble. Late-stage dissolution and dedolomitization also positively affected the reservoir properties of the studied successions. In conclusion, the aforementioned results reveal the impact of various diagenetic processes resulting from magmatic emplacement and their consequent reservoir heterogeneity.

Replacement dolomite occurs in Jurassic Samanasuk Formation in Dara Adam khel area of Kohat ranges, North-Western Himalayas, Pakistan. This study, for the first time, document the process of dolomitization and evolution of strata bound dolomitic bodies. Field investigation, petrography and geochemistry helped in unraveling the formation of several dolomitic bodies. Petrographically dolomites comprises of: (1) medium grain crystalline planer subhedral dolomite (Dol-I); (2) fine grained crystalline anhedral non-planer dolomite rhombs (Dol-II); (3) medium to coarse grained crystalline subhedral-anhedral non-planer dolomite (Dol-III) and coarse to very coarse grained crystalline saddle dolomite cements (SD). The saddle dolomites (SD) postdate the replacement dolomites and precede telogenetic calcite (TC) cements. Stable O and C isotope analysis shows that these dolomites have δ18Ovpdb ranging from -4.09% to -10.4 whereas the δ13Cvpdb ranges from +0.8 to +2.51. Major and trace elements data show that Sr concentrations of 145.5 to 173 ppm; Fe contents of 2198 to 8215 ppm; and Mn contents of 93.5 to 411 ppm. Petrographically replacive dolomites, saddle dolomite, and δ18Ovpdb values depicts neomorphism of replacement dolomites that were formed earlier were exposed to late dolomitizing fluids. As a result of basin uplift during the Himalayan orogeny in Eocene time, dolomitization event was stopped through occurrence of meteoric water. The Main Boundary Thrust (MBT) and its splays were most likely essential conduits that channelized dolomitizing fluids from siliciclastic rocks that were buried deeply into the Jurassic carbonates rocks, leading to more extreme dolomitization.

Dolomitized strata are potential exploration targets because they host economic mineral and hydrocarbon deposits around the globe. Establishing a petrogenetic history for dolomite is thus very vital. In this study, dolomitic bodies present in the Devonian carbonates of Nowshera Formation in Peshawar Basin, North-West Lesser Himalayas in north Pakistan are investigated through field observations, petrographic studies, and geochemical analysis. The carbonates of Nowshera Formation show evidence for multistage dolomitization and a complex diagenetic history. In a first stage the succession was completely dolomitized probably by the reflux of penecontemporaneous mesohaline seawater. This process resulted in both fabric-retentive and fabric-destructive dolomite types under near surface to shallow burial realms. In the subsequent stage saddle dolomites (matrix & cement) were formed under intermediate and/or deep burial realm. This later saddle dolomite phase likely resulted from the circulation of exotic fluids at comparatively high temperature. This local hydrothermal event, evidenced from the fluid inclusion homogenization temperatures, and stable isotopic signatures, also resulted in vuggy, fracture, and dissolution enhanced porosity. Microthermometric analysis of primary fluid inclusions in saddle dolomite confirm the presence of hot (125-178 degrees C) and highly saline brines (17-25 mass% NaCl equivalent). The delta(18)Owater (+2 to +9.2 parts per thousand V-SMOW) calculated from fluid-inclusion homogenization temperatures in conjunction with the comparatively high salinity values is compatible with a magmatic origin of the hydrothermal fluid. It is suggested that the investigated hydrothermal dolomites in the Nowshera Formation formed in Carboniferous-Permian time. During this time, thermal convection heated by the Peshawar Plain Alkaline Igneous Province (PPAIP) may have provided the high temperature and sufficient magnesium (Mg) flux for several millions of years (similar to 40 M.y.), ultimately leading to the formation of hydrothermal dolomite bodies. The pore spaces resulted from the leaching of these hydrothermal fluids were subsequently occluded by meteoric calcite related to the Eocene to Middle Miocene Himalayan exhumation of the studied area. This study provides important implications for potential source of Mg in understanding the genesis and timing of dolomitization.

The ecosystem, biodiversity, and anthropological existence in the Chitral district are in danger due to the sediments and soil erosion stemming from the changes in the land-cover and climate. This research aims to practice the RUSLE model with the changes in the land-cover and climate in upcoming situations for 2030 and 2040 to evaluate soil erosion annually as per the spatial dissemination and the tendency of sediment yield. The multilayer perceptron (MLP), an artificial neural network (ANN), besides the Markov chain analysis was used to model upcoming land-cover. The Max Planck Institute model, which demonstrated a revised bias as well as downscaled grid size under the Representative Concentration Pathways (RCPs), was used for examining the future changes in the climate. The modeled land-cover showed that the areas that are primarily comprised of natural trees and shrubs were transformed largely to agriculture and build-up areas. The average rainfall in the future under different RCP situations was elevated compared to the rainfall through historical time. The continuous variability in the R and C factors affects the probable soil erosion rate and sediment yield. Under RCP8.5 for both future years of 2030 and 2040, the extreme erosion rate was assessed at around 500 and 550 t/ha/year. Additionally, under the different RCP scenarios in 2030 and 2040, the outcomes of sediment yield were more significant than the sediment yield through historical time. The results showed that lower regions of the Chitral district are at risk of amplified soil erosion and sediment yield presently, as shown by the historical data and in the future. The produced soil erosion maps using ArcGIS 10.2 can play a valuable role in managing sustainable development, conservation of the watershed of the Chitral River, and reducing soil loss. Effective measures to overcome these concerns and mitigate the possible effects need to be planned and practiced, particularly the decrease in the storage volume of the reservoirs situated on the river.